What are the sizing criteria for Thoracic Endovascular Aortic Repair (TEVAR) grafts?

TEVAR Graft Sizing Criteria

For thoracic aortic aneurysms, oversize the stent-graft by 10-15% relative to the reference aortic diameter at the landing zones, ensure a minimum landing zone length of 20 mm both proximally and distally, and use contrast-enhanced CT with ≤3 mm slice thickness for pre-procedural measurements. 1, 2

Stent-Graft Diameter Oversizing

For Thoracic Aortic Aneurysms

• Oversize the stent-graft diameter by 10-15% compared to the reference aortic diameter measured at the proximal and distal landing zones. 1, 2
• This 10-15% oversizing provides optimal seal while minimizing complications such as endoleak and stent-graft induced new entry (SINE). 2
• The proximal landing zone should not exceed 40 mm in diameter for standard TEVAR devices. 1, 2

For Type B Aortic Dissection

• Apply minimal to no oversizing (0-10%) when treating type B aortic dissection. 1, 2
• The goal is to cover the proximal entry tear and induce false lumen thrombosis without applying excessive radial force that could worsen the dissection. 1, 2
• Recent research supports that oversizing ≤10% in complicated type B dissection may reduce aortic-related events by up to 50%. 3

Critical caveat: The difference between aneurysm (10-15% oversizing) and dissection (0-10% oversizing) is essential—excessive oversizing in dissection can cause catastrophic complications. 1, 2, 3

Landing Zone Requirements

Minimum Length

• A minimum landing zone length of 20 mm (2 cm) is required both proximally and distally for safe deployment and durable fixation. 1, 2
• This ensures adequate seal and prevents device migration or endoleak. 1, 2

Anatomic Considerations

• Assess the relationship to critical branch vessels, particularly the left subclavian artery and intercostal arteries supplying the spinal cord. 1, 2
• If the landing zone overlaps with the left subclavian artery take-off, plan for embolization or bypass. 1
• Avoid overstenting vessels supplying the major spinal cord in elective settings to prevent spinal cord ischemia. 1

Pre-Procedural Imaging and Measurement

CT Protocol

• Obtain contrast-enhanced CT with ≤3 mm slice thickness of the entire aorta from supra-aortic branches to femoral arteries. 1, 2
• Include both arterial and delayed contrast phases in the protocol. 1
• Use ECG-gated CT for the ascending aorta and proximal arch, as cardiac motion can cause 5-10% variation in diameter between systole and diastole. 1, 2

Measurements to Obtain

• Measure diameters perpendicular to a centerline at the proximal and distal landing zones. 3
• Document the length of the lesion and distances between arch vessels. 1, 2
• Assess iliofemoral artery diameters, calcification, and tortuosity for access planning. 1

High-Risk Anatomic Features

Aortic Tortuosity

• Assess aortic tortuosity at the proximal landing zone, as increased tortuosity significantly predicts type III endoleak, stroke, and all-cause mortality after TEVAR. 1, 2
• High tortuosity in the proximal fixation zone increases risk of endoleak and requires more intensive procedural planning and postoperative surveillance. 1

Aortic Arch Angulation

• Highly angulated or curved arches may prevent proper stent-graft apposition, leading to "bird-beak configuration" and increased risk of type Ia endoleak. 1
• Postprocessing of CT data to measure arch angulation along the centerline can predict which patients are at increased risk. 1
• These patients require closer imaging follow-up to screen for late-developing endoleak. 1

Intraoperative Considerations

Blood Pressure Management

• Reduce systolic blood pressure to <80 mmHg during stent-graft deployment (using nitroprusside, adenosine, or rapid right ventricular pacing) to prevent downstream displacement. 1, 2
• Maintain invasive blood pressure monitoring and control throughout the procedure. 1

Adjunctive Imaging

• Consider intraoperative intravascular ultrasound (IVUS) or transesophageal echocardiography (TOE) for real-time diameter verification, particularly when navigating the true lumen in dissections. 1, 2
• However, recent research suggests IVUS may not significantly impact graft sizing compared to CT-based measurements alone in blunt thoracic aortic injury, though it may reduce stroke risk. 4

Spinal Cord Protection

• Consider preventive cerebrospinal fluid (CSF) drainage in high-risk patients to reduce paraplegia risk. 1

Special Considerations for Highly Tapered Anatomy

• In highly tapered type B dissection (taper >8 mm or taper ratio >20%), consider using proximal tapered stent-grafts plus distal restrictive stent-grafts to match the aortic taper and extend coverage length. 5
• This approach leads to better aortic remodeling compared to standard TEVAR in highly tapered anatomy. 5